Rubbery polymer-acidic carbon black-carboxylic acid mixtures cured with organic peroxides



United States Patent RUBBERY POLYMER-ACIDIC CARBON BLACK- CARBOXYLICACID MEXTURES CURED WITH ORGANIC PEROXIDES Jerry T. Graver and GerardKraus, Bartlesville, Okla,

assignors to Phillips Petroleum Company, a corporation of Delaware NoDrawing. Filed Aug. 7, 1961, Ser. No. 129,524 Claims. (Cl. 260-43) Thisinvention relates to a method of curing polymeric materials to producelow modulus rubber stocks. One aspect of this invention relates to aprocess of reacting polymeric materials and highly acidic carbon blacksin an improved curing system. Another aspect of this inven tion relatesto the resulting cured product of such a process. In a still furtheraspect, this invention relates to a method of utilizing acidic carbonblacks as reinforcing agents for polymeric materials.

For a number of purposes there is a need for low modulus rubbers. Onearea in which there is an increasing demand for such low modulus rubbersis in the manufacture of no squea tires for passenger vehicles. It hasbeen observed that acidic carbon blacks, particularly attrited blacks oflow structure, when used as reinforcing agents in compounding of rubber,results in a marked reduction in the modulus of the cured stock.However, when used in conventional compounding procedures, these acidiccarbon blacks frequently retard the cure.

It has now been discovered that natural rubbers and synthetic rubberssuch as conjugated diene homopolymers, copolymers of conjugated dienesWith compounds containing a vinyl group, and copolymers of monooleiinssuch as ethylene-propylene and ethylene-butadiene copolymers and thelike, combined with highly acidic carbon blacks can be cured to lowmodulus rubbers by the incorporation in the recipe of an organicperoxide and a metal oxide plus a high molecular weight organic acid oran organic peroxide and a metal salt of a high molecular Weight fattyacid.

Therefore, it is an object of the invention to provide an improvedmethod of curing polymeric materials with highly acidic carbon blacks.Another object of this invention is to provide a process whereinpolymeric materials and highly acidic carbon blacks can be reacted withcuratives to produce an improvement in the physical prop erties of thematerial. Another object is to provide a polymeric material havingimproved physical properties as a result of the addition of highlyacidic carbon black and being reacted with a multicomponent curingsystem. Other aspects and several advantages of this invention will beapparent from a study of the disclosure and the appended claims.

. The materials which can be treated for improvements in propertiesaccording to this invention are natural rubber and synthetic rubberypolymers of conjugated diene monomers. Included among these polymers arehomopolymers of conjugated dienes having from 4 to 12 carbon atoms,preferably the polymers of conjugated dienes having 4 to 8 carbon atomsper molecule, such as:

1,3-butadiene Isoprene Piperylene 2-methyl-1,3-pentadienePhenylbutadiene 3 ,4-dimethy1-l,3 -hexadiene 4,5-diethyl-1,3-octadieneChloroprene Fluoroprene I 2-methyl-1,3-hexadiene and the like. Amongthese, butadiene, isoprene and piperylene are preferred. In addition,suitable materials naphthalene, vinyltoluene, heterocyclicnitrogen-contain ing monomers such as pyridine and quinoline derivativescontaining at least one vinyl or alpha-methylvinyl group, such as2-vinylpyridine and 2-methyl-5-vinylpyridine, acrylic andalkacrylic-acid esters, such as methyl acrylate, ethyl acrylate, andmethyl methacrylate, methyl vinyl ether, vinyl chloride, vinylidenechloride, and the like. Polymersv containing acidic groups along thepolymer chain, such as polymers of acrylic acid or methacrylic acidcopolymerized with diene monomers can also be cured with this system.The invention is also applicable to the compounding and curing ofsaturated rubbery polymers such as ethylene-propylene polymers,polyisobutylene and the like.

The metal oxides employed in this invention include the oxides of allmetals of groups IA, II andIH of the Mendeleeff periodic table, thosepreferred being oxides of bivalent metals or polyvalent metals inbivalent state. Typical of these are oxides of magnesium, zinc, cadmium,mercury, calcium, barium, strontium and lead.

The fatty or rosin acid used in the compounding recipe can be added perse or as salts of one of the meals named hereinbefore, it beingunderstood that the metal salt serves as a replacement for the metaloxide and the organic acid. For example, instead of stearic acid andmagnesium oxide, magnesium stearate can be used with equal or betterresults in the cured product. ganic acids employed are those containingfrom 10 to 20 carbon atoms per molecule and include fatty acids such ascapric, lauric, myristic, palmitic, margaric, stearic, arachidic, androsin acids such as abietic acid. In some instances the high molecularWeight acid is added prior to other compounding agents or it may bepresent in the rubber as a residue from the polymerization, thissituation frequently occurring in emulsion polymerized r-ubbers.

Organic peroxides used in conjunction with thisinvention have thegeneral formula:

wherein each R" is selected from the group consisting of alkyl,cycloalkyl, aryl, alkaryl, aralkyl, and acyl radicals containing from 1to 15 carbon atoms. Examples of suitable organic peroxides include:

Dimethyl peroxide Methyl ethyl peroxide Di-tert-butyl peroxideDi-tert-amyl peroxide Di-n-hexyl peroxide n-Butyl n-amyl peroxideDicyclohexyl peroxide Dicyclopentyl peroxide Di(methylcyclohexyl)peroxide Diphenyl peroxide Di-4-tolyl peroxide Di(2,4,6-trimethylphenyl)peroxide Phenyl benzyl peroxide Tert-butyl phenyl peroxide Dibenzoylperoxide Diacetyl peroxide Dibenzyl peroxide Bis(alpha-methylbenzyl)peroxide Bis(alpha-ethylbenzyl) peroxide Bis(alpha-n-propylbenzyl)peroxide Bis(alpha-isopropylbenzyl) peroxideBis(alpha,alpha-dimethylbenzyl) peroxide, also referred to as dicumylperoxide Bis(alpha,alpha-diethylbenzyl) peroxide The preferred or- IBis(alpha,alpha-di-n-propylbenzyl) peroxideBis(alpha,alpha-diisopropylbenzyl) peroxideBis(alpha-methyl-alpha-ethylbenzyl) peroxideBis(alpha-ethyl-alpha-isopropylbenzyl) peroxideBis(alpha-methyl-alpha-tert-butylbenzyl) peroxideBis(alpha,alpha-dimethyl-3-methylbenzyl) peroxideBis(alpha,alpha-diethyl-Z-ethylbenzyl) peroxideBis(alpha-methyl-alpha-ethyl-3-tert-butylbenzyl) peroxideBis(alpha,alpha-dimethyl-2,4-dimethylbenzyl) peroxideBisKalpha,alpha-dimethyl-4-isopropylbenzyl) peroxideBis(alpha,alpha-diisopropyl-4-ethylbenzyl) peroxide The amount of acidiccarbon black used as a reinforcing agent in this invention is generallywithin the range from 20 to 100 parts by weight per 100 parts of polymerwith about 40 to 60 parts being preferable. The amount of the metaloxide or metal salt of the fatty acid used will be in the range from 0.1to 10.0 parts per hundred parts of polymer with 1.0 to 5.0 parts perhundred parts of polymer being preferable. When the organic acid iscompounded per se,.it will be present in the amount of between 0.1 to10.0 parts per hundred parts of polymer. The amount of the'organicperoxide employed is in the range from 0.1 to 10.1 parts per hundredparts of polymer, with 0.25 to 7.5 parts per hundred parts rubber beingpreferable.

The carbon blacks employed in the present invention are those having apH value in the range from 2 to 6. Attrited carbon blacks having acidicproperties may be used in this invention. The term attrited carbonblack-s is used here to define carbon blacks that have been subjected tosevere mechanical treatment, in which the secondary aggregates have beendestroyed. Suitable blacks can be obtained by any of the variousprocesses or treatments known to the art. One procedure by which highlyacidic, low structure carbon blacks can be prepared involves subjectinga furnace black to vigorous milling in the presence of oxygen as in asuccession of passes through a tight roll mill, in a ball mill, an inkmill or by similar means. By such treatment the secondary aggregates arealtered and in the presence of oxygen, acidic properties are impartedthereto. Channel black and furnace blacks oxidized by air or chemicalagents are also applicable in the process if their pH Value falls in therange specified. Y

The pH value of the carbon black used in this invention is measured byASTM procedure D151257T modified by using 25 ml. water per gram ofcarbon black instead of ml. and shortening the heating period to 10minutes after which the water is cooled to room temperature and the pHis measured by use of a Beckman pH meter.

Incorporation of the acidic carbon black and other components of therecipe in the rubber is effected on a roll mill, in a Banbury mixer orby any similar means known to the art. When using the attrited blackshereinbefore disclosed, it is frequently advantageous to add the organicacid or the metal salt or metal oxide to the carbon black prior to thegrinding step, by which means these ingredients are intimately combinedprior to incorporation in the rubbery polymer.

The curing or reacting temperature can vary over a broad range, forexample from 200 to 500 F., although the temperature is generally in therange of 260 to 350 F. The time can also vary considerably from a fewminutes to several hours, although usually a curing time of from 20 to150 minutes is used. One skilled in the art in possession of thisdisclosure, having studied the same, will recognize that it is possibleto vary somewhat the amounts or ratios given, depending upon theparticular polymer, reacting agent and result desired. Thus, thereacting agent or curative can be used in lesser or greater amounts thanthose given but this now is not preferred. Thus, one skilled in the artwill recognize that a basic concept is in the use of the reactant orcurative rather than in the parts by weight when considering the broadaspects of the invention. The temperature at which reaction with thepolymer will take place, though given herein as now preferred, can bevaried somewhat outside the limits given depending upon the particularcircumstances as one skilled in the art in possession of this disclosurewill understand. Thus, the concept of the invention is to bring aboutthe reaction and this one skilled in the art will know how to do, havingstudied this disclosure.

This invention provides a method for converting liquid, semi-solid, andsolid polymers to vulcanized rubbery and cross-linked plastic products.A wide variety of polymer compositions which can be obtained includematerials which are suitable as adhesives, potting compounds, treadstocks, and various types of molded objects.

The following examples are presented in illustration of the invention.However, the specific materials and conditions used are typical only andshould not be construed to limit invention unduly.

Example I A furnace carbon black having a pH value of 8.5 was subjectedto milling alone and in admixture with magnesium oxide. In the firstrun, the black was ball-milled for 16 hours in air following 72 hoursdrying at C. The mill was then opened, and the black was milled oneadditional hour. The pH was 5.2.

In the secondrun, 100 grams of dried furnace carbon black was mixedwith.5 grams of magnesium oxide and ball-milled for 20 hours to producea similar effect as is shown above. The products from these runs weredesignated as Black #1 and Black #2.

Butadiene-styrene rubber having a bound styrene content of about 23.5%and cis-polybutadiene were compounded with these blacks in a peroxiderecipe using biS(oc,oz dimethylbenzyl) peroxide. The butadiene-styrenecopolymer was prepared by emulsion polymerization at approximately 41 F.using a rosin acid soap and coagulated with salt-acid. The rosin acidcontent of the copolymer was about 6% by weight, and the Mooney valuewas (ML4 at 212 F.) 50. Approximate values of the cis-polybutadiene usedin the recipe were: cis content 96%, trans content 1.2%, vinyl content2.8%, Mooney value (ML4 at 212 F.) 45 and an inherent viscosity of 2.35.In these tests the recipe was varied by inclusion of magnesium oxide,stearic acid, and resin 731 (disproportionated pale rosin stable toheatand light). Physical properties were determined on stocks cured 45minutes at 307 F.

From the data shown in Table I, it is demonstrated that when operatingwith a butadiene-styrene rubber, cure was poor in the stock containingthe ball-milled black and that by addition of magnesium oxide asatisfactory cure was realized. When the magnesium oxide was included inthe milling step, tensile strength was improved still more and moduluswas lowered significantly. A comparison of these Values shows thatmodulus is increased without improvement in tensile strength, and heatbuildup is considerably higher in the controls using unmilled blacks.Addition of magnesium oxide to the receipe increases modulus over thatof the control, with little change in tensile or heat buildup whenunmilled black is used. Thus, for these runs, it is apparent. thatlow-modulus stocks having significantly reduced 6 tent 2.8%, Mooneyvalue (ML-4 212 F.) and an inherent viscosity of 2.35. In these testsmagnesium stearate was substituted for the magnesium oxide and stearicacid employed. Data on these tests are shown in Table II. Physicalproperties were determined on stocks cured 45 minutes at 307 F.

This example shows that cis-polybutadiene when compounded withball-milled carbon black, magnesium stearate, and resin 731 has a lowermodulus and lower heat buildup together with increased tensile strengthover the same rubber compounded with unground black.

TABLE II Compounding recipe (parts by Weight) Physical properties RunCarbon Black No. 3 8(1):. Modulus Elonga- Shore Resil- Cis-polydimethyl-Mg Resin 300 percent, Tensile, tion, AT, hardience, butadiene Unmilledbenzyl) stearatc 731 p.s.i. p.s.i. percent F. ness percent #1 furnaceperoxide carbon black heat buildup can be obtained by attrition of theblack and including magnesium oxide in the recipe, preferably bygrinding with the black.

Runs 6, 7 and 8 show that magnesium oxide alone, either introducedseparately or milled with the black, fails to provide an effective curewhen the polymer is cis-poly- A series of tests was made to compare theeffects of zinc and lead stearates with those from the use of magnesiumstearate in compounding cis-polybutadiene containing ball milled carbonblack (Black #1 and cis-poly- TABLE I i Compounding (parts by weight)Physical properties Carbon black Run Butadienc Cis-poly- BiS(a, pt IModulus Ten- Elonga- Shore AT, Resilstyrene butadiene dimethyl- MgOStearic Resin 300 percent, sile, tion, hard- F. ienee,

rubber 1 Unmilled benzyl) Acid 731 p.s.i. p.s.i. percent ness percent #1#2 furnace carperoxide bon black 1. 5 1, 380 2, 780 500 63 60. 8 G9.2 1. 5 1, 210 3, 040 570 62 54. 4 69. 7 1. 5 320 770 680 55. 6 1. 5 1,440 2, 600 500 66 74. 3 63. 5 1. 5 2, 090 2, 680 390 70 70. 9 (i7. 0 1.5 230 360 440 49 47. 6 1. 5 310 580 530 48 50. G 1. 5 190 330 510 46 44.8 1. 5 1, 850 2, 700 410 70 50. 3 77. 8 1. 5 1, 850 2, 540 380 70 54. l'78. 9 1. 5 710 2, 740 690 G0 59. 9 74. 4 1. 5 490 2, 640 810 59 57. 574. 8 1. 5 140 440 780 42 51. 9 1. 5 1, 960 2, 280 340 73 43. 3 82. 5 1.5 1, 480 2, 630 480 68 43. 9 80. 9 1. 5 1, 660 2, 450 420 75 47. 9 82. 4

Butadiene styrene rubber contains approximately 6% by weight, rosin acidfrom polymerization.

2 Materials too soft; to obtain AT using conventional testing methods.butadiene. When stearic acid and resin 731 are included in the recipe,good cure is obtained and stocks having high tensiles and low moduli areobtained.

Example II butadiene described in Example I). Data on these tests r areshown in Table 'III. Curing of test samples was 45 minutes at 307 F.

This example shows that cis-polybutadiene compounded with the ballmilled acidic carbon black and either magnesium stearate, zinc stearateor lead stearate has a lower modulus than a similarly cured polymercompounded with unmilled carbon black and magnesium stearate whilesatisfactory tensile values and satisfactory heat buildup values arealso obtained.

TABLE III Compounding Physical Properties Run No. Unmilled Bis(a,adi-Stearate Modulus Tensile, Elonga- Shore Resilience,

Cis-poly- #1 furnace methylbenzyl 300 percent, p.s.i.. tion, AT, F.hardness percent butadiene carbon black peroxide p.s.i. percent Mg Zn Pb1 Material too soft to obtain AT using conventional testing methods.

7 Examples IV A series of tests was run to test the effects ofball-milled carbon black in ethylene-propylene copolymer rubber. Theball-milled black was Black #1 described in Ex- 0.1 to 10.1 parts byWeight of an organic peroxide having the formula RI! O I wherein each Ris selected from the group consisting of o alkyl, cycloalkyl, aryl,alkaryl, aralkyl, and acyl radicals ample Cunng of test Samples 45mmutes at 307 and contains 1 to carbon atoms and a reactant mate- R P nthese tests Show? Table rial selected from the group consisting of fattyacids and I example Shows that mcorporatlon of acldlc rosin acids, saidorganic acids being present in an amount mlned furnace carbon black 111an '?'P P of from about 0.1 to about 10 parts by weight and havingcopolymer yitllds a lower modulus rubber Wlth a more 10 from 10 throughcarbon atoms per molecule. desirable tensile value and a mole desirableheat buildup 3 A process of heating the resulting mixture of claim valuethan similarly cured polymers using unmilled fur- 2 t produce a cured rd t, nace carbon blacks. 4. A process according to claim 3 wherein thecuring TABLE IV Compounding Physical Properties 113110? Ethylene-Unmilled BiS(a, adi- Stearic Resin Modulus Tensile, Elonga- AT,Resilpropylene #1 furnace methylben- MgO Acid 731 Sulfur 300 percent,p.s.i. tion, F. ience,

copolymer carbon black zyl) peroxide p. .i. Percent percent The term lowmodulus rubber is used. in this distemperature is within the range fromabout 200 to 500 F.

closure to mean a rubber having a modulus of less than and the curingtime is within the range from about 20 about 1200 p.s.i. When speakingof styrene-butadiene coto 150 minutes.

polymer and a modulus of less than about 1000 p.s.i. when 5. A processaccording to claim 3 wherein the curing speaking of ethylene-propylenecopolymer and cis-polytemperature is within the range from about 260 to350 F.

butadiene. and the curing time is within the range from about 30 As manypossible embodiments can be made in this into 60 minutes and wherein theacidic carbon black is vention Without departing from the scope thereof,it is to present in an amount of about 40 to 60 parts by weight beunderstood that all matter herein set forth is to be per 100 parts ofthe polymer. interpreted as illustrative and not as unduly limiting the6. A composition according to claim 2 wherein the said invention.polymeric material is 100 parts butadiene-styrene copoly- We claim: mer,the carbon black hasa pH value of from 4 to 6 1. A process whichcomprises reacting a polymeric ma-- present in an amount of from to 60parts by weight, terial selected from the group consisting of naturalrubber, 40 the organic peroxide is bis( x,u'-dimethylbenzyl) peroxiderubbery homopolymers of conjugated diene monomers present in an amountof from 1 to 2 parts by weight, the having from 4 to 12 carbon atoms permolecule, rubbery metal oxide is magnesium oxide present in an amount ofcopolymers of conjugated diene monomers with comfrom 2 to 3 parts byweight and the organic acid is abietic pounds containing a vinylidenegroup and rubbery satuacid present in an amount of from 0.1 to 10 partsby rated copolymers with an acidic carbon black formed by Weight.grinding carbon black in the presence of oxygen and a 7. A compositionaccording to claim 2 wherein the said metal oxide selected from thegroup of oxides consisting polymeric material is 100 partscis-polybutadiene, the carof magnesium, zinc, cadmium, mercury, calcium,barium, bon black has a pH of from 4 to 6 present inan amount strontium,and lead oxides, the amount of said carbon of from 40 to 60 parts byweight, the organic peroxide is black being at least 20 parts by weightbased upon said bis(u,ot'-dimethylbenzyl) peroxide present in an amountpolymeric material, with about 0.1 to 10.1 parts by weight of from 1 to2 parts by weight, the metal oxide is mag of an organic peroxide havingthe formula nesium oxide present in an amount of from 2 to 3 parts byweight and the organic acid is stearic acid present in R"--O-O- anamount of from 0.1 to 10 parts by weight.

8. A composition according to claim 2 wherein the said wherein each R"is selected from the group consisting of Polymeric material is 100 Partsy -p py e P yal-kyl, cycloalkyl, aryl, alkaryl, aralkyl, and acylradicals mer, the Carbon black has a P Value of fmm 4 f0 6 and contains1 to 15 carbon atoms and at least one mate- Presfint in an amount offrom 40 Parts y Weight, rial selected from the group consisting of fattyacids and the Organic PeTOXide is his y y PemXide rosin acids, theorganic acids having from 10 through 60 P m amount of from 3 t0 5 Partsy Weight, the 20 carbon atoms metal oxide is magnesium oxide present inan amount of 2. Avulcanizable composition obtained by mixing 100 from 2t0 3 Parts y Weight and the Organic acid is Pal-ts by weight f a ol erict i l l t d f stearic acid present in an amount of from 0.1 to 10 partsthe group consisting of natural rubber, rubbery homopolyby weight. mersof conjugated diene monomers having from 4 to 12 9. The compositionprepared by the process of claim 1. carbon atoms, rubbery copolymers ofconjugated diene 10. The composition prepared by the process of claim 3.monomers with compounds containing a vinylidene group and rubberysaturatelgl copolymers, with fro)? ibgut 20 References Cit d b th E minto parts by weig t of an acidic carbon ac aving a pH value of from 2 to6, said acidic carbon black having 70 UNITED. STATES PATENTS been formedby grinding carbon black in the pr nce of 2,442,330 6/1948 Fuller 270s9.5 oxygen and from about 0.1 to about 10 parts by weight 2 737 502 3 det 1 2 23 of at least one metal oxide selected from the gr up f 2, 7, 031 1959 safford et a1, 2 0 oxides consisting of magnesium, zinc, cadmium,mercury calcium, barium, strontium and lead oxides, with about (Otherreferences on following page) UNITED 9 10 STATES PATENTS OTHERREFERENCES Scott 260 Compounding Ingredients for Rubber (1961), pp.Precopio et a1 26094.9 97, 100 and 278. Morrifield 26023.7 Wolf, RubberAge, v01. 80, February 1957, pp. 830 Willis 26041.S 5 and 831. Kirk eta1. 26094.9 Gessler 260-4 1.5 LEON J. BERCOVETZ, Primary Examiner.Adamek et a1. 260 237 X Medalia I 260 949 MILTON STERMAN, Examzner.Gilmont 260 -83.3 10 T. D. KERWIN, R. A. WHITE, Assistant Examiners.

2. A VULCANIZABLE COMPOSITION OBTAINED BY MIXING 100 PARTS BY WEIGHT OFA POLYMERIC MATERIALSELECTED FROM THE GROUP CONSISTING OF NATURALRUBBER, RUBBERY HOMOPOLYMERS OF CONJUGATED DIENE MONOMERS HAVING FROM 4TO 12 CARBON ATOMS, RUBBERY COPOLYMERS OF CONJUGATED DIENE MONOMERS WITHCOMPOUNDS CONTAINING A VINYLIDENE GROUP AND RUBBERY SATURATEDCOPOLYMERS, WITH FROM ABOUT 20 TO 100 PARTS BY WEIGHT OF AN ACIDICCARBON BLACK HAVING A PH VALUE OF FROM 2 TO 6, SAID ACIDIC CARBON BLACKHAVING BEEN FORMED BY GRINDING CARBON BLACK IN THE PRESENCE OF OXYGENAND FROM ABOUT 0.01 TO ABOUT 10 PARTS BY WEIGHT OF AT LEAST ONE METALOXIDE SELECTED FROM THE GROUP OF OXIDES CONSISTING OF MAGNESIUM, ZINC,CADMIUM, MERCURY CALCIUM, BARIUM, STRONTIUM AND LEAD OXIDES, WITH ABOUT0.1 TO 10.1 PARTS BY WEIGHT OF ANORGANIC PEROXIDE HAVING THE FORMULA